Defiance is a science fiction television set on Earth some time after a war with a group of aliens known as the Votans. After a ceasefire is declared after many years of fighting, the majority of organized government on both sides has been destroyed leading to many new factions and militias being created who pursue their own interests. The story focuses on a town known as "Defiance" which stands in the ruins of St. Louis, in which both human and Votan survivors live together.

The series was the first of its kind, in that it was being produced in concert with a massively multiplayer online game by Trion Worlds. Events that occurred in one media would affect the other, and characters would transfer back and forth between the game and television series, which aired for three seasons on SyFy until 2015.